1. Field of the Invention
The invention is directed to a snap fastener suitable for securing a first thin wall such as a housing wall, door leaf, shutter, or the like, which is provided with a through-opening to a second thin wall such as thin-walled wall supports such as housing frames, door frames, wall opening edge, or the like, which is likewise provided with a through-opening, with a base part which can be arranged at the first (or second) thin wall in the through-opening thereof, with a head part extending away from this base part, this head part having a diameter which initially increases and then decreases again in its longitudinal section from the end of the head part in direction of the base part, which head part presents a male plug-in piece which, by overcoming a spring force acting radially outward in direction of the diameter, can be received by an undercut female insertion piece which is formed by or supported by the through-opening of the thin wall, wherein the head part presents a guide or a channel for one or two or more push elements or holding elements which are pressed by at least one spring into a position in which they project over the end of the guide or channel, the ends of which push elements or holding elements projecting out of the guide or the channel have a triangular shape in a projection line extending perpendicular to the thin wall, wherein the base part is formed by a plate overlapping the longitudinal edges of the through-opening in the thin wall, wherein the head part is provided as a housing with fastening projections such as fastening cams (of flexible material) or leaf spring devices having flexible fastening surfaces, which housing can be snapped into a through-opening in one thin wall in such a way that it grips only the one thin wall and that unlocking devices (releasing means) are provided in the housing, by means of which unlocking devices the push elements can be pulled back into the housing from the front and the housing can be disengaged from the other thin wall.
2. Description of Related Art
A snap fastener of the type mentioned above is already known from DE 20 2004 016 009 U1 (see claim 1 and FIGS. 35 to 40C). It is stated in paragraphs [0148] and [0157] that metal panels can be connected to one another by means of the arrangement known from this reference (i.e., the connection element can serve as a substitute for a weld connection), which can lead to discoloration, or for a screw connection or for rivet connections. The snap-in connection can also be used where the back side is difficult to access.
Snap fasteners of this kind which serve as fastening means are also described in the book “D-SNAP technology” (The installation system without screws or tools, innovative fastening for industrial panel processing, Verlag Moderne Industrie, by Ulrich Poestgens, 2006), pages 56 to 60.
In connection with the snap fastening as connection part, it is mentioned that the essential characteristics of a snap fastening in connecting panels to one another particularly include the automatic clamping of the snap elements behind the edges of the installation openings of the two panels and a snug fit in the installation opening. Based on these characteristics, snap fastenings ensure a fixed, vibration-free connection of two (or more) thin walls such as panels. They can be used, for example, to fasten side walls or rear walls to the frame section of a switch cabinet or housing, or to fasten a cover to a panel, or to fasten printed circuit boards to board supports.
A maximum clearance of 0.15 mm between the installation opening and snap fastener is required to ensure that the snap fastener can be inserted through the installation opening without difficulty. Therefore, in theory, there can be a minimal torsion of the panels relative to one another. However, this play can be reduced or entirely eliminated by using two snap fasteners and/or arranging them in the edge area.
Further, it is stated therein that this snap technology offers an alternative to captive screws. When electronic devices are mounted in housings (e.g., server racks), there is a risk that small parts will be lost and cause damage (e.g., by short circuiting in electronic equipment). This led to the development of so-called “captive screws”. With these captive screws, the actual screw fits in a sleeve that is riveted in the outer panel. The inner panel must have a thread cut into it into which the screw can be screwed. If the screw comes loose, it remains anchored in the outer panel thanks to the fixed sleeve and cannot be lost. Disadvantages of captive screws include their high price and very time-consuming installation due to the riveting process. Further, captive screws cannot be easily removed again.
A snap fastener with a total of four snap elements replaces captive screws of this kind. While two opposite snap elements (see the above-cited German Utility Model, FIG. 40A, structural component 1337) produce the fixed connection to the outer panel, the two other opposite snap elements 1322 engage behind the inner panel and can be pulled back by means of an actuating device 43. When disassembled, the captive snap fastener remains fixed in the outer panel due to this design but, in contrast to the above-described screw sleeve for the captive screws, can be disassembled again in a simple manner when required. The snap elements for the fixed connection to the outer individual panel have a much smaller clamping area than those to be opened which must engage behind two panels. Therefore, the installation opening of the inner panel requires cutouts so that the snap elements which fit securely in the outer panel do not slip back through the inner panel into the channels and come loose (see FIG. 38B and FIG. 39B in the Utility Model).
However, when captive screws are replaced by snap technology it has turned out that the removal of a wall held by these snap fastening elements presents difficulties when used a number of times. This is because the plurality of snap fastening elements cannot be exactly aligned simultaneously in such a way that they release the wall simultaneously.